Fluid pressure system

ABSTRACT

A system of valves used in conjunction with a constant-speed pump provides a rate-of-flow-pressure relationship which commences with a high pressure at about zero flow, drops off rapidly to a point of very low flow, then flattens to an approximately straight line, gradually declining pressure to about maximum flow, then drops rapidly to zero pressure at maximum flow. The system includes co-axial, closely spaced and related check valve, pressure relief valve and control valves. The system also includes an adjustable pump by-pass valve and a discharge valve which inactivates the pump motor when discharge pressure exceeds a maximum or falls below a minimum.

United States Patent 1 3,694,105 Martin 51 Sept. 26, 1972 [54] FLUID PRESSURE SYSTEM FOREIGN PATENTS 0R APPLICATIONS Inventor: o s Martin, Micro-Pump 813,572 5/1959 Great Britain ..417/303 Corp., 1021 Shary Court, Concord, Callf- 94520 Primary ExaminerWi1liam L. Freeh 22 Filed: Oct. 2 1970 Attorney-Julian Caplan [21] Appl. No.: 77,527 7 ABSTRACT A system of valves used in conjunction with a con- U-S- n t "417/26, stant speed provides a rate of flow pressure [51] Int. Cl. ..F04b 49/00, F04b 49/08 relationship which commences with a high pressure at [58] Field of Search ..4l7/302-304, 26, about zero fl d p off rapidly to a point of very 417/28 44 low flow, then flattens to an approximately straight line, gradually declining pressure to about maximum [56] References C'ted flow, then drops rapidly to zero pressure at maximum UNITED STATES PATENTS flow. The system includes co-axial, closely spaced and related check valve, pressure relief valve and control Turner valves The ystem also includes an adjustable pump Jolrnsen val e and a discharge valve inactivates Guln' lld et a] a u i ot r wh n discharge pressure exceeds a 3,349,714 10/1967 Grenier ..417/300 maximum or falls below a minimum 3,376,821 4/1968 East ..417/28 3,446,238 5/1969 Norstrud ..417/28 8 Claims, 5 Drawing Figures PATENTED I973 3. 694, l 05 SHEET 1 [IF 2 5115? FIG. 2

\ FIG. 5

INVENTOR. (FLOW 6.2M; THOMAS B.MARTIN MA X.

AT T ORNEYS PATENTED EP 1912 3.694.105 SHEET 2 OF 2 FIG. 4

INVENTOR. THOMAS B. MARTIN BY Q! ATTORNEYS FLUID PRESSURE SYSTEM This invention relates to a new and improved fluid pressure system and more particularly having a gear pump, or the like, driven by a constant speed motor which is energized and de-energized approximately in accordance with the demand for fluid at the discharge end of the system.

Ordinary pumps of this general type with a pressure relief by-pass have pressure-flow characteristics shown in FIG. of the accompanying drawings by the broken lines 91, 94 and 99. The line 91 is too close to horizontal to afford accurate control of the pump, and hence the pump motor cycles on and off frequently. Such frequent cycling has a number of disadvantages, including wear on the switch controls but more particularly is annoying, and in aircraft, where the present'invention has a particular application, may be frightening to passengers. One technique used to avoid frequent cycling of the motor is to steepen the pitch of line 91, but this has the disadvantage of reducing the pressure at the region near full flow of the pump.

Another technique used to avoid the disadvantages of this pump is to employ an accumulator in the discharge line which slows down the cycling, but is annoying. The present invention employs a totally different technique to overcome the disadvantages of constant speed gear pumps which does not have the disadvantages herein above mentioned.

In accordance with the present invention, a constant amount of pressure (indicated by symbol y) is subtracted from the pump discharge pressure except near the zero flow end. This is shown by full line 97 between points 96 and 98. The pump runs steadily at the region indicated by line 97 without off-on cycling of the pump motor. Accordingly, the flow characteristics of the system of the present invention (as distinguished from the flow characteristics of the pump discharge) is indicated by lines 95, 97 and 100, and the pump motor is set to shut off at a pressure indicated by line it.

Another feature of the invention is the fact that the amount of head loss between the pump discharge pressure and the system discharge pressure may be varied by the characteristics of a spring, which spring is easily installed and removed for substitution.

Another feature of the invention is that if expansion of the fluid in the system occurs as, by reason of temperature changes when the pump is shut off, a pressure release valve is provided which allows the fluid to escape back into the inlet reservoir.

Another feature of the invention is that a ball check valve and the control valve which accounts for the differential between the pump and system discharge pressures are physically closely interrelated, are co-axial, and are proximate so that they may be conveniently installed, removed, inspected and serviced.

Another feature of the invention is the provision a valve which shuts off the pump motor and which operates when a maximum desired pressure is exceeded and also when a minimum pressure is indicated, which occurs particularly when the system runs dry. Thus, a single control inactivates the pump drive above a predetermined system discharge pressure or below another predetermined system discharge pressure.

Still another advantage of the invention is the provision of a pressure relief by-pass conduit for the pump which establishes the pump discharge pressure and is insensitive to changes in inlet pressure.

Another feature of the invention is the fact that the system discharge pressure is established at a fixed differential (e.g., 5 psi.) below pump discharge pressure at all times except near zero flow.

Other objects of the present invention will become apparent upon reading the following specification and referring to the accompanying drawings in which similar characters of reference represent corresponding parts in each of the several views.

In the drawings:

FIG. 1 is a schematic cross-sectional view through the system of the present invention, and showing the elements in normal operating condition.

FIG. 2 shows some of the elements in FIG. 1 when the system is under full demand.

FIG. 3 is a view similar to FIG. 2 showing some of the elements of the system at a condition of zero demand.

FIG. 4 shows some of the elements of the system when the fluid supply is exhausted.

FIG. 5 is a schematic diagram showing characteristics of ordinary pumps and the pump system of the present invention plotted to show pressure and flow.

The system of the present invention is shown schematically in the accompanying drawings, FIGS. 14, it being understood that most of the passageways and chambers (with the exception of the pump chamber) are circular in cross section and hence are not here illustrated in detail. The system may be, for convenience, installed in a single metallic block 11 having an inlet passage 12 which leads from a supply reservoir (not shown) at'one end and discharge port 13 at the 0pposite end which leads to one or several variable demands for fluid. In a typical installation, the supply reservoir for inlet port 12 may be a water tank in a pas senger aircraft and the discharge port 13 may be connected to several coffee-makers in the galleys for such an aircraft. It will be understood that demand fluctuates as the water is forced through receptacles containing ground coffee. It further will be understood that the pump capacity can very easily be established to exceed the maximum demand for fluid in the discharge end of the system. Because passengers become annoyed, or sometimes frightened, by off-on cycling of motors, it is desirable to cycle the pump motor as infrequently as possible, and the present invention achieves this end.

To provide access to the interior parts of block 11, openings are formed therein, which said openings may be closed by a bottom plate 14 which is formed with a vent l8 and by top plate 16 which is formed with a vent l7. Closely adjacent inlet port 12 is a filter chamber 21 containing a filter screen 22. Access to chamber 21 to remove filter 22 for cleaning is controlled by a plug 23 threaded into an opening in the bottom of block 1 1.

Inlet passage 24 connects chamber 21 with pump chamber 26, which contains rotatable impellers 27 of the gear pump. One of the impellers 27 is turned by motor 28. Motor 28 is energized from a source of electrical energy and the switch 88 hereinafter described, controls the energization. Extending from pump discharge passage 29 is by-pass passage 31 which leads to by-pass control chamber 32 having a seat 33 near one end which leads back to the inlet side of pump chamber 26. Needle valve 34 cooperates with seat 33 to control by-pass flow of fluid around the pump. Piston 36 on the lower end of valve 34 is provided with a seal 37 which seals the piston in chamber 32. Spring 38 bears against the bottom of piston 36, and the force of said spring 38 is controlled by reason of the fact that the head 39 of adjustment screw 41 bears against the spring. The stem of screw 41 extends through plate 14 and is exteriorly controlled by means of a screwdriver slot 42, or other convenient means.

Normally the pump delivers more flow than the outlets connected to the system require. The excess pump flow is re-circulated through by-pass channel 31 and is used by the pressure regulator assembly to set the pump discharge pressure. In the pressure regulator, atmospheric pressure and spring 38 act together against piston 36 and are opposed by the force of the fluid pressure acting on the opposite side of the piston. Spring 38 is adjustable externally, and the space behind the piston is vented to the atmosphere through vent hole 18. Thus, the pump discharge pressure is set with reference to ambient air pressure by spring 38 and is relatively insensitive to changes in the water pressure supplied at inlet port 12. Normal operation is shown in FIG. 1 where the pressure in conduit 31 exceeds the force of spring 38, and hence the valve 34 is open relative to seat 33. In FIG. 4, however, the pressure in conduit 31 is less than the force of spring 38 and the valve 34 has closed against seat 33, thereby terminating bypass flow through conduit 31.

That portion of the discharge of the pump which does not proceed through the by-pass passage 31 is delivered through passage 29 to control valve chamber 46. Such chamber 46 has a shoulder 47 adjacent to its upper end and is of a smaller diameter above shoulder 47 than below same. Mounted within chamber 46 is an annular liner 48 open at the top and closed at the bottom and having enlarged top and bottom ends provided with top and bottom seals 49 which seal the liner against the walls of chamber 46. Liner 48 has a top opening 51 and a bottom opening 52 which communicates with the area 53 within chamber 46 and between the enlargements at the top and bottom of liner 48.

Slidable within liner 48 is an annular cage 56 divided approximately one-third inward from its upper end by a transverse partition 57 formed with a central opening 58. The upper edge 59 of cage 56 is roughened or serrated so that when said cage 56 is in full-up position as shown in FIG. 3, there is a slight leakage through said serations. Below partition 57 and bearingiagainst the bottom of liner 48 is a spring 61 which forces the cage 56 upwardly. The characteristics of spring 61 determine the pressure drop between the pump discharge pressure and the system discharge pressure as hereinafter explained. Such pressure drop may be varied by changing the spring 61.

Reciprocating in the portion of chamber 46 above shoulder 47 is a holding piston 62 formed with a central opening 63 and the lower end of central opening 63 functions as seat 64. The enlarged diameter portion 66 of piston 62 which is smaller than and reciprocates in the portion of chamber 46 above shoulder 47 is biased downwardly by a spring 67 bearing there-against. The upper seal 49 of liner 48 provides a stop limiting the downward movement of piston 62 and the diameter of portion 66 is less than that of the upper portion of chamber 46 so that when the piston 62 is pushed upward against the force of spring 67 a leakage occurs around the outside of piston portion 66 even though the ball 68 which is interposed between piston 62 and partition 57 is seated against seat 64.

The useful portion of the pump flow passes checkball 68, which is forced back against the opening 58 in partition 57 by the flow. In order to proceed past cage 56, the force of the flow must compress spring 61 allowing cage 56 to move downwardly to the position shown in FIG. 1. The force of spring 61 causes a pressure drop which is indicated in FIG. 5 by reference symbol y and which may, as a typical example, be approximately 5 p.s.i. As a result of this pressure, the system pressure in passage 69 is such differential below that set by the bypass regulator spring 38 whenever there is flow to the outlets connected to discharge port 13.

Connected to passage 69 by duct 74 is a discharge pressure valve chamber 76. The upper end of said chamber 76 is closed by top plate 16. Slidable in chamber 76 is piston 77 which is sealed by means of seal 78 so that the pressure above the seal is atmospheric (by reason of duct 17) and the pressure below is controlled by the pressure in passage 69. Spring 79 interposed between plate 16 and piston 77 biases the same downwardly. There are three positions of piston 77, namely the normal position shown in FIGS. 1 and 2 where the system is operating at normal flow, the fullup position shown in FIG. 3 (where the demand has terminated), and the full-down position shown in FIG. 4 (where the pressure in the system has dropped by reason of, for example, a stoppage in the supply of fluid to the inlet 12), Knob 82 of enlarged diameter is formed but on the upper end of the stem 83 of piston 77. The knob 82 is contacted by switch arm 86 which is pivoted on pivot 87 and bears against micro switch 88. When knob 82 is in mid-position (FIG. 1 switch 88 is closed and motor 28 is energized. However, when piston 77 rises to full upper position (FIG. 3) by reason of the pressure in passage 69 exceeding the force of spring 79, the switch arm 86 pivots clockwise, switch 88 is opened, and motor 28 and pump 26 stopped. Similarly, when the system pressure drops, piston 77 drops to the position shown in FIG. 4 and again the switch 88 is opened.

In normal operation, whenever there is a flow to the fluid outlets connected to discharge port 13, the pressure in cylinder 76 is normal, i.e., it is balanced by spring 79 so that the piston is in mid-position. Gear pump 26 is operational and the excess supply of the pump passes through by-pass passage 31.

When the demand at discharge port 13 diminishes (see FIG. 2), cage 56 is moved by spring 61 to restrict the flow past ball 68, thereby maintaining the pressure drop of approximately 5 p.s.i., as before. This condition holds even though the flow is reduced to a trickle. However, when the flow stops completely, the fit between the end 59 of cage 56 and the seat 64 is not good enough to maintain the pressure drop. Thereupon, with the pump still nmning, the pressure in the passage 31 begins to increase, approaching that set by the spring 38. This increase in pressure also increases in cylinder 76 causing piston 77 to rise against the force of spring 79 to the position shown in FIG. 3, whereupon switch 88 is opened and the motor 28 de-energized.

When the pump is stopped, there is a slight back-flow due to the imperfect fitting of the impellers 27 in chamber 26. Such back-flow enables the ball 68 (which is of very low density comparable to that of the fluid in the system, since the ball may be made of nylon or similar material) to seat firmly in seat 64, holding the pump discharge pressure in the system and maintaining switch 88 off.

In any sealed liquid system, there is always the possibility of an increase in fluid pressure through temperature changes, etc. The present invention provides a pressure release valve (FIG. 3). Spring 67 is calibrated to hold enlargement 66 of piston 62 against the upper seal 49. If a pressure rise occurs beyond seal 49 which exceeds the force of spring 67, piston 62 rises out of contact with upper seal 49. Since the diameter of upper end 66 is less than that of chamber 46, a back-flow may occur back through the impellers 27 (which leak somewhat) and back through inlet port 12. At such higher pressures, the piston 77 is restrained by the cover 16 against further movement.

If for any reason the system pressure approaches zero (see FIG. 4), piston 77 drops to the bottom of chamber 76, being impelled by spring 79. The cam knob 82 is disengaged from switch arm 86 de-energizing motor 28. This prevents the pump from running dry or from running under any condition when it cannot maintain some pressure in the system to the outlet 13. An auxiliary manual starting switch (not shown) is provided to energize the motor for the purpose of establishing initial pressure in the system. Once the system pressure is established, the operation is automatic. The pump runs steady when water is flowing to outlet 13 and stops only when all-outlets are closed.

Directing attention now to FIG. 5, the pressure in passage 29 is indicated by lines 91, 94 and 99. However, the pressure in passage 69 is indicated by lines 95, 97 and 100. Line xx is determined by the force of spring 79 and cuts off motor 28 when the pressure rises above line-xx by reason of a closing off of the outlets which are connected to port 13. It will be noted that to the right of point 96, the line 97 is parallel to the line 91 but is displaced in an amount of pressure indicated by reference symbol y. This pressure difference is established by the force of spring 61 (which may be interchanged with another spring of different characteristics upon removal of plate 14). Normally, as the outlets below port 13 open and close the pressure and flow move along line 97. When cage 56 is in full upward position, there is a flow past seat 64 by reason of the unevenness at the upper end 59 of piston 66 and this accounts for the upward inclination of line 95 to the left of point 96. When the pressure exceeds the intersection of line x-x with line 95, then motor 28 is deenergized. It is thus seen that the normal outlet demands at the outlet port 13 cause a flow and pressure relationship shown by line 97 in FIG. 5. Only when the flow approaches zero does the motor shut off, and hence cycling of the motor is minimized.

What is claimed is:

1. A fluid pressure system wherein fluid pressure is increased to a pump pressure and then reduced in pressure to a discharge pressure which is a predetermined differential below pump pressure except when flow through the system approaches zero, said system comprising a pump, a prime mover driving said pump, first means for maintaining pump discharge pressure below a pro-selected maximum, second means for reducing pressure by the amount of said differential and having a chamber on the discharge side of said pump, said chamber having a seat, a reciprocating member in said chamber formed with a cage having a closed position against said seat substantially, but not completely, blocking flow through said chamber and an open position permitting flow through said chamber, said member moved towards open position by pump pressure of said fluid, a check ball within said cage, said ball when engaging said seat restraining back flow through said chamber toward said pump and maintaining pressure in said system beyond said second means at system discharge pressure when said drive of said pump is interrupted and demand from said system is zero, resilient means biasing said member to closed position whereby, when fluid at pump pressure forces said member to open position, the force required to overcome the force of said resilient means causes a drop in the discharge pressure of said system, said drop being a differential below pump pressure dependent upon the characteristics of said resilient means, and third means responsive to discharge pressure in said system beyond said chamber to interrupt driving of said pump by said prime mover when said discharge pressure exceeds a predetermined pressure by reason of said flow being so small as to pass between said seat and said member without moving said member against the force of said resilient means.

2. A system according to claim 1 on which said first means comprises means forming a by-pass around said pump and having a second seat, a valve head cooperable with said second seat to control flow through said by-pass, and second resilient means biasing said head toward said second seat.

3. A system according to claim 1 in which said reciprocating member is formed with openings in its surface engaging said seat to permit fluid flow past said seat at very low volume substantially at pump pressure when said member is in closed position.

4. A system according to claim 1 in which said cage is formed with a second seat, said ball movable responsive to direction of fluid flow to engage either said first mentioned seat when said pump is not operating or said second seat when said pump is operating.

5. A system according to claim 1 which further comprises an annular piston reciprocable within said chamber and formed with said first-mentioned seat and movable between a closed position sealing against said chamber wall and an open position, second resilient means biasing said piston toward closed position, said piston dimensioned relative to said chamber whereby when said ball is seated on said seat and the back pressure in the system beyond said second means exceeds the force of said second resilient means said piston is moved to open position to permit reverse flow of fluid through said chamber back to said pump to relieve said back pressure.

6. A system according to claim 5 in which each of said chamber, reciprocating members, piston and ball are coaxial relative to a common axis, said member, piston and ball moving on said axis.

7. A system according to claim 1 in which said third means comprises means forming a discharge pressure chamber in fluid communication with the outlet of said first-mentioned chamber, a piston reciprocable within said second chamber and having a cam extending to the exterior of said second chamber, second resilient means biasing said piston toward extended position, a cam follower positioned to be engaged by said cam, and fourth means associated with said cam follower, said piston movable to retracted position against the force of said second resilient means when the discharge pressure exceeds said predetermined pressure and said cam and cam follower operable when said piston is in retracted position to actuate said fourth means to inter- 8 rupt driving of said pump.

8. A system according to claim 7 in which said piston is movable in said second chamber by the force of said second resilient means to a second extended position beyond said first-mentioned extended position when the pressure in said second chamber drops below a predetermined pressure, said cam and cam follower operable when said piston is in second extended position to actuate said fourth means to interrupt driving of said pump. 

1. A fluid pressure system wherein fluid pressure is increased to a pump pressure and then reduced in pressure to a discharge pressure which is a predetermined differential below pump pressure except when flow through the system approaches zero, said system comprising a pump, a prime mover driving said pump, first means for maintaining pump discharge pressure below a preselected maximum, second means for reducing pressure by the amount of said differential and having a chamber on the discharge side of said pump, said chamber having a seat, a reciprocating member in said chamber formed with a cage having a closed position against said seat substantially, but not completely, blocking flow through said chamber and an open position permitting flow through said chamber, said member moved towards open position by pump pressure of said fluid, a check ball within said cage, said ball when engaging said seat restraining back flow through said chamber toward said pump and maintaining pressure in said system beyond said second means at system discharge pressure when said drive of said pump is interrupted and demand from said system is zero, resilient means biasing said member to closed position whereby, when fluid at pump pressure forces said member to open position, the force required to overcome the force of said resilient means causes a drop in the discharge pressure of said system, said drop being a differential below pump pressure dependent upon the characteristics of said resilient means, and third means responsive to discharge pressure in said system beyond said chamber to interrupt driving of said pump by said prime mover when said discharge pressure exceeds a predetermined pressure by reason of said flow being so small as to pass between said seat and said member without moving said member against the force of said resilient means.
 2. A system according to claim 1 on which said first means comprises means forming a by-pass around said pump and having a second seat, a valve head cooperable with said second seat to control flow through said by-pass, and second resilient means biasing said head toward said second seat.
 3. A system according to claim 1 in which said reciprocating member is formed with openings in its surface engaging said seat to permit fluid flow past said seat at very low volume substantially at pump pressure when said member is in closed position.
 4. A system according to claim 1 in which said cage is formed with a second seat, said ball movable responsive to direction of fluid flow to engage either said first mentioned seat when said pump is not operating or said second seat when said pump is operating.
 5. A system according to claim 1 which further comprises an annular piston reciprocable within said chamber and formed with said first-mentioned seat and movable between a closed position sealing against said chamber wall and an open position, second resilient means biasing said piston toward closed position, said piston dimensioned relative to said chamber whereby when said ball is seated on said seat and the back pressure in the system beyond said second means exceeds the force of said second resilient means said piston is moved to open position to permit reverse flow of fluid through said chamber back to said pump to relieve said back pressure.
 6. A system according to claim 5 in which each of said chamber, reciprocating members, piston and ball are coaxial relative to a common axis, said member, piston and ball moving on said axis.
 7. A system according to claim 1 in which said third means comprises means forming a discharge pressure chamber in fluid communication with the outlet of said first-mentioned chamber, a piston reciprocable within said second chamber and having a cam extending to the exterior of said second chamber, second resilient means biasing said piston toward extended position, a cam follower positioned to be engaged by said cam, and fourth means associated with said cam follower, said piston movable to retracted position against the force of said second resilient means when the discharge pressure exceeds said predetermined pressure and said cam and cam follower operable when said piston is in retracted position to actuate said fourth means to interrupt driving of said pump.
 8. A system according to claim 7 in which said piston is movable in said second chamber by the force of said second resilient means to a second extended position beyond said first-mentioned extended position when the pressure in said second chamber drops below a predetermined pressure, said cam and cam follower operable when said piston is in second extended position to actuate said fourth means to interrupt driving of said pump. 